1. Field of the Invention:
This invention relates to a gear motor and more particularly to a hydraulic gear motor used for driving a ventilator by rotating in response to actuation by a high pressure actuating oil from an oil pump.
2. Description of the Related Art:
A conventional gear motor of this type is, for example, disclosed in Japanese Patent Laid Open No. 62 (1987) - 276274. There, the gear motor is provided with a housing having inlet and outlet ports for the fluid, an inner tooth gear rotatably disposed within the housing and forming actuating chambers therein, an outer tooth gear disposed within the inner gear and forming the above-mentioned actuating chambers together with the inner tooth gear, a shaft integrally rotated with the outer tooth gear, a bearing rotatably supporting the shaft, and inlet and outlet ports communicating with the actuating chambers. A brake which can be contacted with the inner tooth gear is slidably disposed in the housing and an electromagnetic coil is provided for displacing the brake shoe.
However, a port is not formed at a housing side of the gears. As a result, the outer and inner tooth gears are pressed toward the housing side by oil pressure, a clearance between the cover and the tooth gears oil becomes large and the leakage amount of the high pressure oil increases. That is, the tooth gears are contacted with the housing side by the oil pressure, so that the oil does not flow into a clearance between the housing and the gears. The oil film between the housing and the gears is thus eliminated and the sliding resistance becomes large. The motor cannot be rotated (oil lock state) when the sliding resistance becomes larger than the torque generated by the motor.